Dopamine has been implicated in many roles in behavioral and cognitive functions. For example, changes in dopamine levels regulate important components of reward pathways in the brain. Current theories suggest that addictive drugs such as cocaine and alcohol stimulate these pathways in the same manner as natural rewards like food and sex. Dopamine is found throughout the animal kingdom, and studies on invertebrates suggest that many of its functions are highly conserved. In insects, as in mammals, dopamine acts as a neuromodulator via interactions with different dopamine receptor types that are found on the surface of dopamine responsive nerve cells. Activation of these receptors by ligand binding may lead to changes in gene expression and ion channel permeability. Insects are good models for investigating the molecular mechanisms of dopamine action because they have simpler nervous systems than mammals, and yet display many complex behaviors. The honey bee, Apis mellifera, is particularly good for these investigations because of its ability to learn simpler as well as more complex associations in its environment. Furthermore, the honeybee genome has been sequenced, which will provide detailed genomic information for future studies. Two distinct honeybee D1-like dopamine receptors have been cloned. The work proposed here will provide insight into the molecular mechanisms through which dopamine acts by investigating the roles of both D1-like receptors in motor control, sensory perception and associative learning. Preliminary evidence suggests that RNA interference (RNAi) can be used to disrupt expression of each dopamine receptor in the brain.
The specific aims of this proposal are to use RNAi to reduce levels of one, or both, of the dopamine receptors and then analyze bees for predictable changes in nonassociative and associative behaviors. Motor function will be examined by analysis of the well characterized feeding motor program. Changes in sensory (taste) perception will be assayed by determining sucrose response thresholds. Both association and recall will be examined using associative olfactory learning. Because each receptor has distinct expression patterns and different functional characteristics, it is possible that each receptor will affect the assayed behaviors in different ways. This work is intended to further develop the use of RNAi in the insect brain and to provide the groundwork for detailed analysis of the contributions of each dopamine receptor to learning.
